<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        @keyframes rotate {
  0% {
    transform: rotate(0deg);
  }
  100% {
    transform: rotate(360deg);
  }
}
.gradient {
  --size: 250px;
  --speed: 50s;
  --easing: cubic-bezier(0.8, 0.2, 0.2, 0.8);
  width: var(--size);
  height: var(--size);
  filter: blur(calc(var(--size) / 5));
  background-image: linear-gradient(rgba(55, 235, 169, 0.85), #5b37eb);
  animation: rotate var(--speed) var(--easing) alternate infinite;
  border-radius: 30% 70% 70% 30%/30% 30% 70% 70%;
}

@media (min-width: 720px) {
  .gradient {
    --size: 500px;
  }
}
body {
  background-color: #222;
  position: absolute;
  inset: 0;
  display: flex;
  place-content: center;
  align-items: center;
  overflow: hidden;
}

/* This is just to transition when you change the viewport size. */
* {
  transition: all 0.25s ease-out;
}
    </style>
</head>
<body>
    <div class="gradient"></div>
</body>
</html>